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This undated handout image provided by the Agriculture Department shows the bacterium, Enterococcus faecalis, which lives in the human gut. The bacterial zoo inside your gut could look very different if you're a vegetarian or an Atkins dieter, a couch potato or an athlete, fat or thin. Now for a fee and a stool sample, the curious can find out just what's living in their intestines and help one of the hottest new fields in science. (AP Photo/Agriculture Department)

This undated handout image provided by the Agriculture Department shows the bacterium, Enterococcus faecalis, which lives in the human gut. The bacterial zoo inside your gut could look very different if you're a vegetarian or an Atkins dieter, a couch potato or an athlete, fat or thin. Now for a fee and a stool sample, the curious can find out just what's living in their intestines and help one of the hottest new fields in science. (AP Photo/Agriculture Department)